A gallium nitride (GaN)-based compound semiconductor is a direct transition type semiconductor, and can control a wavelength from visible rays to ultraviolet rays. The gallium nitride-based compound semiconductor has high thermal and chemical stabilities and high electron mobility and saturated electron velocity. The gallium nitride-based compound semiconductor has excellent physical properties such as a large energy band gap as compared to known gallium arsenic (GaAs) and indium phosphorus (InP)-based compound semiconductors. On the basis of the aforementioned properties, an application range thereof is expanded to optical devices such as light emitting diodes (LED) of a visible ray region and laser diodes (LD), and electronic devices used for the next-generation wireless communication and satellite communication systems requiring high power and high frequency properties, which are fields having a limitation in known compound semiconductors.
Light emitting properties of the gallium nitride-based light emitting device depend on an active layer formed of indium gallium nitride (InGaN) or indium aluminum gallium nitride (InAlGaN) and a p-type contact layer to emit light from the active layer to the outside. However, it is difficult to increase internal quantum efficiency due to lattice mismatching between the active layer and the contact layer, and a difference in growth temperature.
Particularly, since an insulating sapphire substrate is used, an electrode structure where n-type and p-type electrodes exist on the same plane is formed, such that a current crowding phenomenon easily occurs. In the case of p-type gallium nitride (GaN), it is difficult to perform a current diffusion due to properties of high thin film resistance and low mobility. This acts as a main factor reducing device properties due to nonuniform light emitting property and heat generation. Accordingly, there is an urgent demand for various device structures and manufacturing processes to manufacture a high-power and large-area light emitting device.